用光子相关光谱法测量多分散颗粒系的颗粒粒度分布

光子相关光谱 ( Photon Correlation Spectroscopy,简称 PCS)技术是测量亚微米及纳米颗粒粒度的有效方法 ,其测量原理始基于颗粒的布朗运动。设计完成了 PCS颗粒粒度测量装置 ,并进行多分散颗粒系的粒度分布测量 ,测量结果与样品标称值相吻合     

微光探测装置自成暗室设计开发

针对现有微光检测系统体积大、避光效果差等不足,对微光探测装置进行全新设计。采用反应杯与光探测头自成暗室,减少暗室进出机构,提高避光效果;采用斩波法扣除本底计数,从而消除背景光引起的测量误差。性能测试结果显示:该微光探测装置的光子本底计数小于等于200光子/s,测光上限平均值达到1.1×107光子/s,变异系数(CV)小于等于3%,达到目前现有的微光检测系统的技术指标要求,可用于化学发光免疫分析仪等需要进行微光信号检测的精密仪器开发,对基于微光探测技术的仪器行业的发展具有重要意义。     

SIPM在脉冲光检测系统中的应用研究

为了实现硅光电倍增管(silicon photomultiplier,SIPM)对超出光子计数极限的微弱脉冲光信号的测量,建立了基于SIPM积分工作模式的脉冲光检测系统。测试了SIPM在同一光信号照射下,偏置电压与增益以及信噪比之间的关系,并测试了同一增益条件下,SIPM对不同光信号的响应特性。结果表明:SIPM在积分工作模式下,其增益可以达到104以上,并随着偏置电压的增加而指数增长;其信噪比也随着电压的增加而增加,在光强比较微弱的情况下,SIPM对光强是线性响应的。所设计的系统可以在一定程度上替代光电倍增管进行微弱脉冲光信号的测量。     

Application of a high power Yb fiber‐based laser compatible with commercial optical parametric oscillator for coherent anti‐stokes raman scattering microscopy

Coherent anti‐Stokes Raman scattering (CARS) microscopy is a powerful tool for chemical analysis at a subcellular level, frequently used for imaging lipid dynamics in living cells. We report a high‐power picosecond fiber‐based laser and its application for optical parametric oscillator (OPO) pumping and CARS microscopy. This fiber‐based laser has been carefully characterized. It produces 5 ps pulses with 0.8 nm spectral width at a 1,030 nm wavelength with more than 10 W of average power at 80 MHz repetition rate; these spectral and temporal properties can be slightly modified. We then study the influence of these modifications on the spectral and temporal properties of the OPO. We find that the OPO system generates a weakly spectrally chirped signal beam constituted of 3 ps pulses with 0.4 nm spectral width tunable from 790 to 930 nm optimal for CARS imaging. The frequency doubling unconverted part is composed of 7–8 ps pulses with 0.75 nm spectral width compatible with CARS imaging. We also study the influence of the fiber laser properties on the CARS signal generated by distilled water. In agreement with theory, we find that shorter temporal pulses allow higher peak powers and thus higher CARS signal, if the spectral widths are less than 10 cm^?1. We demonstrate that this source is suitable for performing CARS imaging of living cells during several hours without photodamages. We finally demonstrate CARS imaging on more complex aquatic organisms called copepods (micro‐crustaceans), on which we distinguish morphological details and lipid reserves. Microsc. Res. Tech. 77:422–430, 2014. © 2014 Wiley Periodicals, Inc.     

Multiphoton microscopic imaging of adipose tissue based on second-harmonic generation and two-photon excited fluorescence

The fresh adipose tissue was investigated by the use of multiphoton microscopy (MPM) based on two-photon excited fluorescence and second-harmonic generation (SHG). Microstructure of collagen and adipose cells in the adipose tissue is clearly imaged at a subcellular level with the excitation light wavelengths of 850 and 730 nm, respectively. The emission spectrum of collagen SHG signal and NADH and FAD fluorescence signal can also be obtained, which can be used to quantify the content of collagen and adipose cells and reflect the degree of pathological changes when comparing normal tissue with abnormal adipose tissue in the same condition. The results indicate that MPM has the potential to be applied to investigate the adipose tissue and can be used in the research field of lipid and connective tissues.     

Ultrafast optical pulse delivery with fibers for nonlinear microscopy

Nonlinear microscopies including multiphoton excitation fluorescence microscopy and multiple-harmonic generation microscopy have recently gained popularity for cellular and tissue imaging. The optimization of these imaging methods for minimally invasive use requires optical fibers to conduct light into tight space, where free-space delivery is difficult. The delivery of high-peak power laser pulses with optical fibers is limited by dispersion resulting from nonlinear refractive index responses. In this article, we characterize a variety of commonly used optical fibers in terms of how they affect pulse profile and imaging performance of nonlinear microscopy; the following parameters are quantified: spectral bandwidth and temporal pulse width, two-photon excitation efficiency, and optical resolution. A theoretical explanation for the measured performance of these fibers is also provided.     

Autofluorescence spectroscopy and imaging of Platymonas subcordiformis irradiated by diode laser based on LSCM

Autofluorescence spectra and optical imaging of Platymonas subcordiformis after irradiation of diode laser were observed via laser scanning confocal microscopy (LSCM). With 488 nm Ar(+) laser excitation, the horizontal and vertical dimensions of a cup-shaped chloroplast of the irradiation group increased about 10% compared with the control group. The fluorescence spectra were similar between irradiation group and control group with a maximum fluorescence band around 682 nm, whereas the former has a higher intensity. Image of a small circular substance with stronger two-photon autofluorescence (TPA) was obtained when using two-photon excitation wavelength of 800 nm in single-channel mode. Further analysis by the 800 nm excitation based on two independent-channels mode showed an emission band of the small circular substance around 376-505 nm, which corresponded to the eyespot of P. subcordiformis. In lambda scanning mode, with two-photon wavelength of 800 nm excitation, six fluorescence peaks that are located at 465, 520, 560, 617, 660 and 680 nm were observed; the fluorescence intensity of the irradiation group was higher than that of the control group, especially at 520, 560 and 617 nm. As a conclusion, diode laser irradiation can promote chloroplast growth of P. subcordiformis cells in the form of expanding area and the increasing content of protein, phospholipids and chlorophyll. LSCM, especially TPA imaging based on femtosecond laser excitation, provides a nondestructive, real-time and accurate method to study changes of living algal cells under laser irradiation and other environmental factors.     

硼碳氮薄膜的制备与表征

用电子束蒸发的方法在单晶硅(100)基片上制备了硼碳氮薄膜,通过椭圆偏振仪、X射线衍射仪(XRD)、X光电子能谱仪(XPS)、傅立叶红外光谱仪(FTIR),测试分析了薄膜厚度均匀性、成分与结构.结果表明,薄膜均匀性较好,薄膜的沉积速率非常慢;薄膜在衬底温度为常温下沉积已是晶态的,随着衬底温度升高到450 ℃,其结晶性逐渐增强;薄膜不是石墨与BN的混和膜而是C、B、N相互结合成键.     

Optimal parameters in variable‐velocity scanning luminescence lifetime microscopy

We determine the optimal parameters (scan velocities) for measuring the luminescence lifetime on the microsecond scale using the recently introduced method based on scanning the excitation beam across the sample. Using simulations, we evaluate the standard deviation and bias of the luminescence decay rate determined by scanning with two different velocities. The analysis is performed for Poisson‐ and normal‐distributed signals, representing different types of detection techniques. We also show that a weak uncorrected background induces a bias in the obtained decay rate, and take this effect into account when choosing optimal measurement parameters. For comparison, the analysis is additionally performed for two conventional gating schemes for lifetime measurement. The variable‐velocity scanning method is found to be more robust to the effect of the background signal than the gating schemes.     

数据保真项与稀疏约束项相融合的稀疏重建

本文针对低光子计数成像过程中产生的泊松高斯混合噪声,提出了一种数据保真项与稀疏约束项相融合的稀疏重建方法。首先,基于泊松高斯噪声相互独立的混合噪声模型,建立了数据保真项与稀疏约束项相融合的稀疏重建目标函数;在图像块聚类的基础上,应用改进贪婪算法实现类内稀疏分解和字典更新;最后,稀疏分解和字典更新交替迭代求解干净图像。针对强烈泊松高斯噪声污染图像的重建实验显示,本文方法与对比方法相比,重建结果的PSNR值平均提升了5.5%,MSSIM值也有明显提升。这些结果表明:本文方法对具有强烈泊松高斯混合噪声的图像有较好的图像复原和噪声去除效果。